1. Field of the Invention
The present invention relates to devices for controlling the optical focus and alignment of optical beams, such devices being particularly useful in apparatus adapted to optically write and read with optical data-storage media, e.g., optical discs.
2. Description of the Prior Art
Various apparatus utilize means for manipulating an optical light path, e.g., to focus and/or align a beam of light such as a laser beam. One illustrative system is an optical record and playback apparatus which optically writes and reads information in the form of tracks of very small (e.g., a micron or less in size), optically detectable marks on a storage medium. In the writing and reading of such marks it is necessary to maintain the active light beam precisely focused at a predetermined plane of the information media. Such media, typically in the form of a rotatable disc, are moved, e.g. rotated, relative to the active light beam to effect scanning of the beam along tracks of the media; and it is necessary also that the beam be properly aligned relative to the track position both in writing and reading operations.
Thus, in the above-described and other analogous applications, servo mechanisms often are provided to maintain the precise focus and alignment that is required for proper operation. Such mechanisms typically will include sensor systems which detect improper focus or misalignment of the active light beam(s). In optical disc systems such misalignment can include radial non-alignments (improper position of the beam in a direction radial to the center of rotation for the disc) and tangential non-alignments (improper position of the beam in a direction forward or backward along the concentric or spiral tracks of the disc).
Signals from such sensor systems typically are fed to electromechanical transducers, which adjust the position of one or more of the elements that define the beam's optical path, to correct the improper focus or misalignment of the light beam. One conventional type of transducer for providing such adjustment is an electro-magnetic transducer incorporating a loudspeaker-type coil which is adapted to move an armature that is connected to a lens or reflective element of the beam's path defining means. U.S. Pat. No. 4,135,206 discloses a system wherein a lens barrel is supported by a resilient element for movement normal to the record medium surface (to allow focus adjustment in response to first coil means located near one end of the lens barrel) and for tilting movement about a point near the bottom of the lens barrel (to allow radial and tangential tracking adjustment in response to four other coils located around the opposite end of the lens barrel). All required adjustments can be accomplished by this system; however, it is relatively complex in construction and therefore costly to fabricate and bulky in form.
Piezoelectric bender elements have recently been developed in forms that are relatively compact and inexpensive to fabricate, and it has been suggested that these elements may be useful in controlling the movement of mirrors to effect beam adjustment in such optical systems. Also commonly assigned U.S. patent application Ser. No. 193,771, now U.S. Pat. No. 4,291,958, entitled "Camera With Electronic Flash and Piezoelectric Lens Motor" and filed Oct. 3, 1980, in the names of L. F. Frank and J. K. Lee and U.S. patent application Ser. No. 194,323, now U.S. Pat. No. 4,303,324, entitled "Annular Piezoelectric Plastic Bender Lens Motor" and filed Oct. 6, 1980, in the name of M. A. Marcus disclose various advantageous piezoelectric bender configurations for controlling focus in photographic apparatus. The present invention follows the approach of simplifying focus and tracking control of such optical systems by the use of piezoelectric bender structures.